In general, berries are naturally high in antioxidants — compounds that may slow cancer growth. The darker the berry, the greater its phytochemical content and the more likely its reputed health benefits. But this doesn't necessarily mean eating them will stave off cancer or other chronic diseases, said Jeffrey Blumberg, director of the Antioxidants Research Laboratory at Tufts University. A variety of factors come into play, including "how many berries are being consumed, over what period of time, and in the context of one's dietary pattern and other risk factors for disease," he said. Here's some of what we know.

Blueberries

What we know: One of the few naturally blue-hued foods humans eat, blueberries are packed with antioxidant power, which comes from high levels of anthocyanins, a type of flavonoid or plant compound. They also contain significant amounts of micronutrients and fiber.

Emerging research: Blueberries have been shown to improve insulin sensitivity in overweight men and women, and lower blood pressure levels in pre-diabetic men and women without raising blood sugar.

The key may be the anthocyanins, which have been shown in several laboratory-based animal and cell studies to cause blood vessels to relax and increase production of nitric oxide that helps in maintaining normal blood pressure, said Dr. Arpita Basu, an assistant professor of nutrition at Oklahoma State University.

Berries also have anti-inflammatory effects and may be a memory-protecting food. The resveratrol found in blueberries may help prevent macular degeneration, a disease of the retina and the leading cause of blindness in people older than 65, according to vision researchers at Washington University School of Medicine in St. Louis. Like the cranberry, blueberries might help prevent bladder infections by preventing bacteria from attaching to the walls of the bladder, according to the National Institutes of Health.

Noted: Billberries, a close cousin of the blueberry, have been shown to promote eye health and protect against glaucoma and cataract progression. Processing the berries can cause a significant decrease in the anthocyanin content.

Raspberries

What's inside: A high-fiber powerhouse, raspberries also have calcium, magnesium, phosphorus, potassium, vitamin C and bone-building vitamin K. They also are a good source of several B vitamins, including folic acid and niacin.

Emerging research: Raspberries have higher levels of ellagic acid than strawberries; ellagic acid has been shown "to be a powerful antioxidant and toxic to cancer cells," said Basu. They may also be a natural treatment for arthritis, due to their high anthocyanin content. Researchers showed black raspberries, which have antioxidant, anti-cancer and anti-inflammatory properties, can prevent also colorectal tumors in animal studies.

Noted: Before freezing, add some lemon juice to help them maintain their color

Cranberries

What's inside: A close relative of the blueberry, cranberries have the same blue-red anthocyanin flavonoids. The tart, red berry is an excellent source of vitamin C and fiber, as well as a good source of manganese and copper.

Emerging research: The compounds in cranberries called "proanthocyanidins" may prevent bacteria, such as E. coli, from clinging to the cells along the walls of the urinary tract and causing infection, said Dr. Catherine Neto, an associate professor of chemistry at the University of Massachusetts at Dartmouth.

Cranberries may reduce the ability of H. pylori bacteria to live in the stomach and cause ulcers and reduce dental plaque. Neto's research has shown in cell cultures, cranberry compounds reduce the growth and proliferation of breast, prostate and colon tumor cells. Cranberry treatment reduces bladder cancer and lymphoma, animal studies suggest.

Noted: Dried cranberries are high in calories — 370 per cup. Bottled cranberry drinks and cranberry cocktails are usually loaded with added sugar. Drink it unsweetened; mix with half a glass of apple juice.

Strawberries

What's inside: The only fruit to flaunt its seeds on the outside, strawberries are an excellent source of vitamins C and K, dietary fiber, flavonoids (anthocyanidins) and the plant compound ellagic acid. They also contain calcium, magnesium, phosphorus and potassium.

Emerging research: Strawberries are also potent antioxidants and have been shown to reduce cardiovascular risk factors in several animal and human studies, such as elevated blood pressure, hyperglycemia and inflammation, said Basu. Supplementing with freeze dried strawberries can improve bad cholesterol levels in people with metabolic syndrome, according to Basu's research. In animals, ellagic acid inhibited the growth of tumors caused by certain carcinogens.

Noted: Consider buying organic; strawberries are among the most heavily sprayed with pesticides and other agricultural chemicals. They can also cause allergic reactions. They retain more of their vitamin C content if left whole.

Acai (Ah-sigh-ee) berries

What's inside: The round, purple-black fruit, which tastes like a blend of berries and slightly bitter chocolate, is packed with antioxidants, essential fatty acids and fiber. It also contains iron, calcium fiber and heart-healthy fats.

Emerging research: The antioxidant power depends on how the berry is eaten. Straight acai has the most nutrients, but it's not available in the U.S. Some cosmetics and beauty products contain acai oil on the ingredient list, but there's no evidence of health benefits. "There is limited evidence for benefit beyond what most other berries can provide," said Nancy Cohen, head of the Department of Nutrition at the University of Massachusetts at Amherst.

Noted: Beware There's no evidence the berries promote weight loss any more than any other fruits. Because fresh acai is only available in the Amazon rainforest of Brazil, look for it in juice or pulp form or powder. Just two tablespoons of powder — sprinkled on cereal, yogurt or smoothies — meets the suggested daily dose of antioxidants. Heating it may diminish some of its antioxidants.

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